Swapped to Overlay sidebar for more intuitive UI

App/UI/MainWindow.xml

@@ -9,10 +9,17 @@
     <object class="AdwBreakpoint">
       <condition>max-width: 500sp</condition>
       <setter object="split_view" property="collapsed">True</setter>
+      <setter object="show_sidebar_button" property="visible">True</setter>
     </object>
   </child>
   <property name="content">
-    <object class="AdwNavigationSplitView" id="split_view">
+    <object class="AdwOverlaySplitView" id="split_view">
+      <property name="min-sidebar-width">200</property>
+      <property name="max-sidebar-width">200</property>
+      <property name="show-sidebar"  
+            bind-source="show_sidebar_button"  
+            bind-property="active"  
+            bind-flags="sync-create|bidirectional"/>
       <property name="sidebar">
         <object class="AdwNavigationPage">
           <property name="title" translatable="yes">Sidebar</property>
@@ -36,7 +43,15 @@
           <property name="child">
             <object class="AdwToolbarView">
               <child type="top">
-                <object class="AdwHeaderBar" />
+                <object class="AdwHeaderBar">
+                  <child type="start">  
+                    <object class="GtkToggleButton" id="show_sidebar_button">  
+                      <property name="icon-name">sidebar-show-symbolic</property>  
+                      <property name="active">True</property>  
+                      <property name="visible">False</property>
+                    </object>  
+                  </child>
+                </object>
               </child>
               <property name="content">
                 <object class="GtkLabel">